Speedy stars may be galactic immigrants

HOW does a hypervelocity star gain its high speed? For those clustered in the constellation Leo, it could be because they are immigrants from another galaxy.

It is widely believed that all hypervelocity stars in our galaxy became so speedy by being catapulted from the Milky Way's heart by the colossal black hole present there. Mario Abadi of the Cordoba Observatory in Argentina and colleagues were intrigued as to why more than half of them are found in Leo, and they built a computer model to find out. This suggests that the stars may be the remains of a dwarf galaxy that the Milky Way's gravitational pull tugged into a long, thin strand 150 million years ago, and that the heat this generated accelerated the stars to their huge speeds (www.arxiv.org/abs/0810.1429).

The researchers concede that the idea is a long shot. It would be bolstered if the ...

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